Previously ultrastructural studies have shown that B. pertussis has a crystalline surface lattice consisting of a 40 kDa porin protein. We have developed large scale methods for the purification of this protein in order to study the structural and functional characteristics of this protein. Porin protein was purified by sequential extractions of cell envelopes with Triton X-100 and Zwittergent 3-14 followed by DEAE ion-exchange chromatography. NH2-terminal amino acid analysis of the purified porin was performed and an oligonucleotide was constructed from this sequence. This DNA fragment was used to probe a lgt11 library of B. pertussis DNA and a clone was identified that consists of a truncated porin gene containing the N-terminal portion of the protein. A second clone was identified that would encode for the remainder of the gene. Identification of the porin gene will allow further molecular studies on the structure and function of this outer membrane protein. Three hybridomas were established that appear to recognize the monomeric form of the porin and are presently being characterized. The ability of purified porin to function as a protective antigen in the mouse aerosol model for pertussis is being investigated.